An internal combustion engine for a vehicle has a specific resonance rotation speed region that is dependent on an engine mount and a drive system damper.
JP2001-123857A, published by the Japan Patent Office in 2001, proposes a variable effective compression ratio internal combustion engine for a vehicle in which the variable compression ratio of the internal combustion engine is suppressed to be small in the resonance rotation speed region.
In this prior art, when the rotation speed is within the resonance rotation speed range during start-up of the internal combustion engine, torque variation is reduced by suppressing the effective compression ratio of the internal combustion engine to be small. By reducing torque variation during start-up, the amplitude of torsional vibration in a crankshaft of the internal combustion engine and vibration in a main body of the internal combustion engine is reduced.
When the rotation speed of the internal combustion engine increases beyond the resonance rotation speed range in this prior art, the effective compression ratio is increased to an effective compression ratio for a normal operation and combustion is begun in the internal combustion engine.